1. Field of the Invention
This invention relates to a magnetoresistive reproduce head, and in particular to a dual element magnetoresistive head.
2. Description Relative to the Prior Art
The magnetoresistive (MR) reproduce head has gained wide acceptance in the magnetic recording field since it was disclosed in U.S. Pat. No. 3,493,694, issued to Hunt in 1970. The MR head is characterized by high output and low noise, making it particularly attractive for reproducing short wavelength signals. It may be fabricated by thin film deposition techniques allowing the relatively inexpensive manufacture of multitrack heads with narrow track widths for high density recording applications. A variety of shielded and unshielded configurations using single and dual MR elements and incorporating a number of biasing techniques are known in the art.
Dual element MR heads are disclosed in U.S. Pat. No. 3,860,965 entitled "Magnetoresistive Read Head Assembly Having Matched Elements for Common Mode Rejection", issued in the name of Voegli and U.S. Pat. No. 4,878,140 entitled, "Magnetoresistive Sensor with Opposing Currents for Reading Perpendicularly Recorded Media", issued in the names of Gill et al. The heads disclosed in these patents comprise parallel MR elements separated by thin electrically insulating layers. It has long been known in the art, that MR structures such as the above, whose elements are separated by thin electrically insulating spacers are subject to shorting problems. Such shorting may be due to pin holes in the insulating spacer, or may occur in head lapping, or during head operation when the abrasive magnetic tape being reproduced can smear the soft MR element across the spacer, shorting it to adjacent conductive material. This has occurred, for example, in heads utilizing soft adjacent layer biasing where an MR element is separated by an thin electrically insulating spacer from a conductive magnetic material whose magnetic field induces the bias in the MR element. Bajorek et al, recognizing the problem in their U.S. Pat. No. 4,024,489 entitled "Magnetoresistive Sandwich including Sensor Electrically Parallel with Electrical Shunt and Magnetic Biasing Layers", teach overcoming the problem by intentionally shorting the MR sensing layer and the magnetic biasing layer by use of a very thin (220 angstrom), contiguous conductive separation layer. However, the structure disclosed by Bajorek et al, is stated to result in a 30% loss of signal from the single MR sensor for a given energy dissipation in the head because the current flowing through the conductive shunting layer provides no contribution to signal output.